1. Field of the Invention
This invention relates to a novel recording liquid for use in recording with an ink, and particularly to a recording liquid suitable for a recording system comprising discharging a recording liquid from a fine discharge outlet (discharge orifice) provided on a recording head and throwing the recording liquid as droplets, thereby carrying out recording without any clogging in the recording means.
2. Description of the Prior Art
The conventional writing implements (fountain pens, felt pens, etc.) as recording means for recording on a material to be recorded, such as paper and the like, use solutions of various dyes in water or organic solvents as an ink.
Even the so called ink jet recording system, according to which recording is carried out by discharging a liquid from a recording head through a discharge orifice by oscillation of a piezooscillator or by an electrostatic attraction caused by application of a high voltage, uses solutions of various dyes in water or an organic solvent. However, the recording liquid for the ink jet recording has more stringent requirements for so many characteristics than those for inks for the ordinary writing implements such as fountain pens and felt pens.
The ink jet recording is to throw droplets of a recording liquid, the so called "ink", for their deposition on a material to be recorded and to carry out recording. Such a recording liquid comprises a recording agent (for which a dye or a pigment is used) and a liquid medium for dissolving or dispersing the recording agent (for which water or various organic solvents or their mixtures are used) as basic components, and, if necessary, can further contain various additives.
So far known recording liquids are solutions or dispersions of various dyes or pigments in an aqueous or non-aqueous solvent, as disclosed, for example, in Japanese Patent Publications Nos. 8361/1975 40484/1976, 13126/1977 and 13127/1977 and Japanese Laid-Open Patent Application No. 95008/1975.
Desirable requirements for these recording liquids are that
(1) they must have liquid physical properties (viscosity, surface tension, electroconductivity, etc.) which are matched to the discharge conditions (driving voltage for piezoelectric members, driving frequency, shape of orifice and quality of material of the orifice, orifice diameter, etc.),
(2) they must be stable and must undergo no clogging even when they are stored for a long time,
(3) they must have a rapid fixing and smooth dot peripheries and less bleeding,
(4) the printed image must have a clear color tone and a high density,
(5) the printed image must have a good water resistance and a good light fastness,
(6) they must not attack the surrounding members (containers, joint tubes, seal materials etc.), and
(7) they must have an excellent safety against a bad smell, toxicity, inflammability, etc.
It is quite difficult to satisfy the said requirements at the same time, and it can be said that the said prior art is not satisfactory for this reason.
A recording liquid applicable to the said desired recording basically comprises a dye and its solvent, as described above, and thus the characteristics of the recording liquid greatly depend on the properties specific to the components used as a dye and a liquid medium. Accordingly, it is a very important technique in the relevant technical field to select a dye and a liquid medium so that the recording liquid can satisfy the said requirements. Above all, there has been no known recording liquid, based on a yellow dye, which can fully satisfy the said requirements.
To increase an effect of preventing clogging at a recording liquid discharge outlet due to deposition of inorganic salts, a stability of the recording liquid, and an effect of preventing corrosion of metal constitution members in writing implements, inorganic salts such as NaCl, Na.sub.2 SO.sub.4, and the like, and ions such as Ca.sup.++ and the like are removed from a dye, for example, to 5% or less by weight of NaCl and 1% or less by weight of Na.sub.2 SO.sub.4, by ultrafiltration, ion exchange resin treatment, or organic solvent treatment, or together with salting out or acid deposition treatment. However, when such treatments are applied to a yellow dye, typical of which are C.I. Direct Yellow-86 and its derivatives, the chemical and physical characteristics of the dye itself are inevitably changed, and it has been found that the stability and long time storage property of a recording liquid containing such a dye are considerably deteriorated with a failure to obtain the desired effects.
The structure of a yellow dye, typical of which are C.I. Direct Yellow-86 and its derivative, as herein referred to, includes the following structural formula (B) registered as C.I. Direct Yellow-86 in Color Index, the following general structural formula (A) covering the formula (B), and structures covering those having --SO.sub.3 Li or --SO.sub.3 K in place of --SO.sub.3 Na in the structural formulae (A) or (B). ##STR2##
Relevant phenomena as problems will be described in detail below.
Water or mixture of water with various water-soluble organic solvents have been so far used as a liquid media for the recording liquid, and preferable liquid media which can form a recording liquid satisfying all the said requirements for a recording liquid fairly well include mixtures of water with a glycol such as ethyleneglycol, diethyleneglycol, and the like. The phenomena as problems seem to be due to a considerable decrease in the solubility of the Yellow dye in such liquid media after the said treatment.
As a result of extensive studies, the present invention has been established by finding dyes suitable for the desired recording liquid, which have a excellent solubility in liquid media comprising a mixture of water with a glycol and have less contents of inorganic salts causing clogging, etc.
It has been known that the dye of structural formula (A) has several distinguished basic characteristics such as a clear color phase, a good light fastness, a high water resistance, and the like, and also has disadvantages in the solubility in the liquid media and the preservability of the resulting recording liquid, and has not been fully utilized practically yet. These problems have been completely solved in the present invention.